An artery is one of the tube-shaped blood vessels that carry blood away from the heart to the body's tissues and organs. An artery is made up of an outer fibrous layer, a smooth muscle layer, a connecting tissue layer, and the inner lining cells. If arterial walls become hardened due to the accumulation of fatty substances, then blood flow can be diminished. Hardening of the arteries, or loss of vessel elasticity, is termed arteriosclerosis while fatty deposit build-up is termed atherosclerosis. Atherosclerosis and its complications are a major cause of death in the United States. Heart and brain diseases are often the direct result of this accumulation of fatty substances that impair the arteries' ability to nourish vital body organs.
Balloon angioplasty is a nonsurgical method of clearing coronary and other arteries, blocked by atherosclerotic plaque, fibrous and fatty deposits on the walls of arteries. A catheter with a balloon-like tip is threaded up from the arm or groin through the artery until it reaches the blocked area. The balloon is then inflated, flattening the plaque and increasing the diameter of the blood vessel opening. The arterial passage is thus widened. As a result of enlarging the hardened plaque, cracks may unfortunately occur within the plaque to expose the underlying fresh tissue or cells to the blood stream.
There are limitations, however, to this technique's application, depending on the extent of the disease, the blood flow through the artery, and the part of the anatomy and the particular vessels involved. Plaque build-up and/or severe re-stenosis recurs within 6 months is up to 30-40 percent of those treated. Balloon angioplasty can only be characterized as a moderate-success procedure. Recently, a newer technique of inserting a metallic stenting element is used to permanently maintain the walls of the vessel treated at its extended opening state. Vascular stents are tiny mesh tubes made of stainless steel or other metals and are used by heart surgeons to prop open the weak inner walls of diseased arteries. They are often used in conjunction with balloon angioplasty to prevent restenosis after the clogged arteries are treated. Stenting technique reduces the probability of restenosis; however, the success rate is still sub-optimal. The underlying fresh tissue or cells still pose as a precursor for vessel reclosures or angio-spasm.
When a clogged artery is widened, the plaque is broken up and the underlying collagen or damaged endothelium is exposed to the blood flow. Collagen has a pro-thrombotic property that is part of body's healing processes. Unless the collagen or the damaged endothelium is passivated or modulated, the chance for blood vessel clotting as well as restenosis exist. Moderate heat is known to tighten and shrink the collagen tissue as illustrated in U.S. Pat. No. 5,456,662 and U.S. Pat. No. 5,546,954. It is also clinically verified that thermal energy is capable of denaturing the tissue and modulating the collagenous molecules in such a way that treated tissue becomes more resilient ("The Next Wave in Minimally Invasive Surgery" MD&DI pp. 36-44, August 1998). Therefore, it becomes imperative to post-treat vessels walls after the walls are treated with angioplasty and/or stenting procedures.
One method of reducing the size of cellular tissues in situ has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to the tissues, and causes them to shrink and tighten. U.S. Pat. No. 5,775,338 to Hastings discloses a heated perfusion balloon for reduction of restenosis. It can be performed on a minimal invasive fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective. However, the heat supplied by a heated perfusion balloon cannot exceed a blood cells' destructive temperature around 42 to 45.degree. C.; the thermal effectiveness of this low temperature range is inadequate to treat the fresh collagen or denuded endothelium after blood vessel enlargement procedures. An alternate ablative treatment apparatus using a RF technique shall have an advantage because of the use of a therapeutic energy that is rapidly dissipated and reduced to a non-destructive level by conduction and convection, to other natural processes.
RF therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. Radiofrequency energy, when coupled with a temperature control mechanism, can be supplied precisely to the apparatus-to-tissues contact site to obtain the desired temperature for treating a tissue.
A stent deployed within a vessel, such as a coronary stent, has excellent metal-to-tissue contact surface. It becomes an ideal medium for applying thermal energy to the tissue needed for treatment or modulation. In the case of angioplasty alone, the enlarged blood vessel still needs certain metallic contact surface for delivering the RF thermal energy to the denuded collagen or damaged endothelium. A temporary metallic stenting element is useful in this case to shrink and tighten the target tissue. Several patents disclose a basket-type electrode catheter or a loop-type electrode catheter. Examples are U.S. PAT. No. 5,100,423 to Fearnot; U.S. Pat. No. 5,255,679 to Imran; U.S. Pat. No. 5,263,493 to Avitall; U.S. Pat. No. 5,345,936 to Pomeranz et al.; U.S. Pat. No. 5,411,025 to Webster, Jr.; U.S. Pat. No. 5,465,717 to Imran et al.; U.S. Pat. No. 5,555,883 to Avitall; U.S. Pat. No. 5,569,244 to Hahnen; U.S. Pat. No. 5,628,313 to Webster, Jr.; U.S. Pat. No. 5,730,704 to Avitall; U.S. Pat. No. 5,738,683 to Osypka; U.S. Pat. No. 5,772,590 to Webster, Jr.; U.S. Pat. No. 5,820,568 to Willis. However, none of the above-referred patents discloses an elevate and enlarged conductive surface which are expandable/collapsible to contact the implanted stent for effective transmission of RF current to said implanted stent.
Therefore, there is a need for an improved medical apparatus having the capability to effectively contact the inner walls of a tubular vessel using the radiofrequency energy to treat an enlarged artery or other tissues, such as esophagus, larynx, uterus, urethra and the like.